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3. DEVELOPING RIVER WATER BODY ENVIRONMENTAL STANDARDS 3.1 Defining Indices of Hydrological Alteration Stage 1 of the Project R

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3. DEVELOPING RIVER WATER BODY ENVIRONMENTAL STANDARDS 3.1 Defining Indices of Hydrological Alteration Stage 1 of the Project R SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 3. DEVELOPING RIVER WATER BODY ENVIRONMENTAL STANDARDS 3.1 Defining indices of hydrological alteration Stage 1 of the project reviewed environmental standards and parameters included a literature review to identify the full range of parameters for both rivers and lakes that may need to be controlled and the circumstances in which they are significant. In tandem with this work, a review and appraisal of existing standards, both within the UK and internationally was carried out to determine where there are any gaps – i.e. any parameters that have been identified as relevant but for which there are no existing UK or international standards available. The results of Stage 1 were presented in a report, whose main conclusions were: • Most countries have various methods of determining environmental flows, each defined for a different purpose, e.g. scoping or impact assessment. • Licensing of reservoir releases and abstractions present quite different problems, and different methods have been developed to deal with these issues. With reservoir releases, the flow regime is likely to be subject to significant management (apart from very large floods that by-pass the dam), since it needs to be created. Abstractions, by and large, have no impact on high flows and so the focus is on low flow impacts. • Where data are scarce, expert opinion is used, and increasingly a formal structured approach to getting consensus amongst a group of experts, including academics and practitioners, is favoured. • There is wide acceptance that all parts of the flow regime have some ecological importance. As a result, there is a growing move away from single low flow indices towards environmental flows. • Many methods determine environmental flows in relation to the natural flow regime of the river. Some methods define flow in terms of site characteristics, such as flow per unit width needed for salmon migration in Lancashire, but it has not been possible to examine the data or the basis of these derivations. Other methods define environmental requirements in terms of more direct hydromorphological elements, such as water depth and velocity. • Small scale studies have shown that flow interacts with morphology to define physical habitat (such as width, depth, velocity and substrate) for specific organisms. These quality elements vary spatially; water is deep in pools and shallow on riffles; velocity is high in riffles and low in pools. Standards based on these quality elements at the broad water body scale cannot be readily defined. To implement standards at the reach scale, site data are essential. • Implementation of the WFD will require that environmental standards are applied for all water bodies regardless of hydrological and ecological data available. Consequently, standards are required that can be applied without having to visit the water body or collect excessive data. This means that standards must be related to parameters that can be obtained from maps or digital databases, such as river flow, catchment area or geology. Any resulting standards will have less predictive power at a local scale and cannot be tested using site data. • A hierarchical approach may be needed in which a broad scale approach, perhaps based on flow, is used as a screening tool to assess all water bodies. A more detailed approach, perhaps based on depth or velocity, may be applied to a smaller number of sites identified as requiring close attention. • The natural flow regime is complex and is characterised by timing, magnitude, duration and frequency; all of which are important for different aspects of the river ecosystem. To produce operational standards, there is a need to identify a 38 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 small number of parameters that capture its most significant characteristics. For example the number of high flow events greater than three times the median flow has been shown to be related to the structure of macrophyte and macro- invertebrate communities in New Zealand (Clausen, 1997). The main outcome of Stage 1 was that the regulatory parameter for environmental standards for rivers at a broad scale should be flow, since data on potentially more ecological meaningful parameters, such as depth and velocity are not widely monitored and cannot be determined without detailed surveys at all sites. Since flow varies greatly between water bodies, generic flow standards need to be expressed in dimensionless terms, such as proportions of natural flow or unit flow per drainage area or channel width. Nevertheless, UK agencies should develop a hierarchical approach to standards, where broad scale methods based on flow are used for screening, but detailed scale methods based on more directly ecologically meaningful parameters, such as depth and velocity, are used for site level impact assessment and license setting. The flow regime of a river or level regime of a lake is often a complex time-series, rising and falling in response to precipitation, snowmelt, geology and catchment conditions. Many of the methods used around the world to set environmental standards for water resources are based on the premise that freshwater aquatic ecosystems are adapted to natural variations in the hydrological regime and are thus dependent upon them. For example, the Building Block Methodology (BBM) developed in South Africa (Tharme and King, 1998; King et al. 2000) recognises that river ecosystems are reliant on basic elements (building blocks) of the flow regime, including low flows (that provide a minimum habitat for species, and prevent invasive species), medium flows (that sort river sediments, and stimulate fish migration and spawning) and floods (that maintain channel structure and allow movement onto floodplain habitats). Richter et al (1996) analysed the magnitude (of both high and low flows), timing (indexed by monthly statistics), frequency (number of events), duration (indexed by moving average minima and maxima) and rate of change of natural flow regimes. They defined 32 parameters that were considered to be relevant to the river ecosystem. This was reduced to 8 key parameters in a redundancy analysis (Poff et al., 2000) as many of the 32 original indices were inter- correlated. Richter et al further suggested that initial flow management targets could be that all parameters should be within 1 standard deviation from the natural mean. The method has been adapted for analysis of Scottish rivers by Black et al (2000). However, precise ecological relevance of these parameters has not been defined and the 1 standard deviation threshold has never been tested. Alterations to the hydrological regime due to abstractions, impoundments, diversions and river basin transfers can have very diverse impacts on any of these indices depending on their type, infrastructure and operation. To make the process of defining environmental standards for water resources manageable, it is necessary to organise all the possible hydrological alterations into a few scenarios for which ecosystem impacts can be analysed. The simplest approach is to consider two scenarios of hydrological alteration: (1) abstraction (directly from the river or aquifer supplying the river) and (2) impoundment where abstracted water is taken from a reservoir. (1) Abstraction Abstraction licenses may be complex, allowing different volumes to be taken at different times and according to different hydrological conditions. However, we will consider only a constant abstraction of a fixed volume of water, which will reduce the entire regime. Figure 20 shows a natural river regime (in blue) and the regime for the 39 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 same period given a constant abstraction of 0.06 m3s-1. It is evident that the abstraction is having a greater proportional impact at low flows; it is having no impact on timing of floods and very little impact on their magnitude. Because of this, the focus of environmental standards to manage abstractions is on low flows. 1.800 1.600 1.400 1.200 1.000 flow 0.800 0.600 0.400 0.200 0.000 01/01/1986 20/02/1986 11/04/1986 31/05/1986 20/07/1986 08/09/1986 28/10/1986 17/12/1986 date Figure 20 River flow regimes: natural (blue) and impacted by a constant abstraction of 0.06 m3s-1 (pink) (2) Impoundment Impoundments can have even more complex impacts on the hydrological regime than abstractions depending on the size of the weir or dam, settings of sluice gates or release structures, level and size of spillways and dam operation. However, to make the exercise manageable we will consider a single impoundment scenario. Figure 21 shows the same natural flow regime (in blue) as Figure 20 and the regime for the same period with an impoundment in place. In this case, there is a constant compensation flow release from the dam of 0.13 m3s-1. It can be seen that in the late summer/early autumn the compensation flow is greater than the natural flow. Major floods in February, April and December pass the dam via the spillway. However, small floods in late Spring, Summer and Autumn disappear from the hydrograph as water is stored in the reservoir. 40 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 1.800 1.600 1.400 1.200 1.000 flow 0.800 0.600 0.400 0.200 0.000 01/01/1986 20/02/1986 11/04/1986 31/05/1986 20/07/1986 08/09/1986 28/10/1986 17/12/1986 date Figure 21 River flow regimes: natural (blue) and impacted by an impoundment with a constant compensation flow of 0.13 m3s-1 (pink) The two scenarios require different types of management: restrictive and active (Acreman and Dunbar, 2004). Abstraction needs restrictive management, in which environmental protection is achieved by restriction of practices by, for example, a “hands-off” flow (HOF) (Barker & Kirmond, 1998) where abstraction is permitted provided that the flow is above a certain critical value, but must reduce or cease when the flow falls below this value.
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